An efficient PAPR analysis of OFDMA for cellular communications

In this paper, we propose a new PAPR reduction by using a partial transmit sequences (PTS) method with coded side information (SI) technique. These methods are used in an orthogonal frequency division multiplexing (OFDM) system. The OFDM employs orthogonal sub-carriers for data modulation. These sub-carriers unexpectedly present a large peak to average power ratio (PAPR) in some cases. In order to reduce PAPR, the sequence of input data is partitioned into disjoint sub-block of PTS. If number of sub-block increases, high efficiency of PAPR reduction can be obtained. However, a quite large calculation cost must be demanded and thus it is impossible to obtain the optimum PTS. In the proposed method, we introduce a coded side information technique assuming the pseudo-optimum condition into the PTS. The total calculation cost becomes drastically reduced and side information bits for recovering original data in demodulation. In simulation results, the proposed method demonstrated the improvement of PAPR and bit error rate (BER) performance.

A new family of low density parity-check (LDPC) codes, called as invertible subset LDPC (IS-LDPC) codes, was proposed for peak-to-average power ratio (PAPR) reduction in OFDM systems recently. In this paper, we propose a PAPR reduction scheme for orthogonal frequency-division multiple access (OFDMA) systems based on IS-LDPC codes. The proposed scheme maps the invertible subsets of IS-LDPC codewords onto subcarriers to construct invertible symbol subsets. Then, the invertible symbol subsets are inverted independently for reducing the PAPR of downlink OFDMA systems. There is no need to transmit the side information by extra channels, which significantly reduces the system overhead and eases the system design. Simulation results show that the PAPR reduction scheme based on IS-LDPC codes produces remarkable PAPR reduction performance and good error correction performance in downlink OFDMA systems. Therefore, the proposed PAPR reduction scheme could be an efficient solution to reduce the PAPR of downlink OFDMA systems.

High peak-to-average-power ratio (PAPR) is a particular disadvantage of orthogonal frequency-division multiplexing (OFDM) systems and can significantly degrade the power efficiency at the transmitter. The aim of this paper is to propose a post-inverse fast Fourier transform (IFFT) PAPR reduction method based on intelligent linear symbol combining with the objective to minimize the PAPR at the transmitter. Unlike the methods so far reported in the literature, the proposed method has a relatively low complexity and does not require external randomization sequences. This paper will also investigate the impact of the proposed method on the system's bit error rate (BER) performance and provide a closed-form analytical expression that takes into account the BER dependency on the side information bits and multiblock combination. It will be shown that the proposed technique can provide significant PAPR reductions at manageable levels of signal processing requirements while the BER degradation is relatively small.

The multiple access scheme for the long term evolution (LTE) physical layer is based on Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink. The main drawback of OFDMA is the peak-to-average power ratio (PAPR) problem. Dummy sequence insertion (DSI) concept can be an efficient PAPR reduction method for the LTE downlink system because it is very simple to implement and side information is not needed. However, the DSI has to sacrifice a decrease in the transmitted data rate for a large number of dummy subcarriers. In this paper, a novel approach to the DSI concept is proposed for complete application to an LTE system. For effective utilization of physical resources, the unused space of the LTE system is calculated, and dummy subcarriers are inserted into the unused space. Therefore, there is no degradation in transmitted data rate. Simulation results show that the proposed method can reduce PAPR considerably without degradation of bit error rate (BER) performance as a LTE downlink system.

One of the major drawbacks of multi-carrier systems is the high peak-to-average power ratio (PAPR) of the transmitted signals. In this paper, the proposed novel low-complexity selective mapping (SLM) and partial transmit sequences (PTS) schemes are applicable to interleaved orthogonal frequency division multiple access (OFDMA) uplink systems for PAPR reduction. The basic idea is to explore the special structure of interleaved OFDMA, so as to reduce the complexity of PAPR reduction. Current PAPR reduction techniques can be combined with the proposed structure, SLM and PTS are combined for instance. Simulation results show that compared with traditional techniques, the proposed technique can gain the same PAPR reduction but with considerable complexity reduction. The new SLM interleaved OFDMA scheme reduces the computational complexity, while it shows almost the same performance of PAPR reduction as that of the conventional SLM interleaved OFDMA scheme, the new PTS proposed can reduce the complexity too. This method needs side information in the receptor.

Blind selective mapping for single-carrier frequency division multiple access system

OFDM has Major disadvantage is that it leads to high Peak to Average Power Ratio (PAPR) which is consider to be as the main implementation drawback. In this paper we are discussing about PAPR which affects the performance and efficiency of Power Amplifier (PA) and its influence by utilizing the Selective Mapping (SLM) technique in OFDM system for reduction of PAPR. the idea for improved SLM produces several independent signals based on converting the original data lock into many independent signal and then the signal has lowest PAPR that specific signal is transmitted. Also data rate trade-off exist at the receiver end when side information is detected for the recovery of data block. which leads to the reduction of data rate. Improved SLM techniques for reducing the PAPR is the most promising reduction technique in its non-uniform phase factor for PAPR reduction in multicarrier OFDM system. Furthermore the estimate expression by using Complementary Cumulative Distribution Function (CCDF) for PAPR has been discussed. Simulated results demonstrate that OFDMA signals using improved SLM technique carried significant effects in reduction of PAPR in OFDM system.

In this paper, we consider the high peak-to-average power ratio (PAPR) problem of non-contiguous orthogonal frequency division multiplexing (NC-OFDM) signals in cognitive radio systems. A high PAPR can lead to saturation in the power amplifier (PA) of secondary users (SUs) and consequently increase spectral spreading, and cause interference to adjacent primary users (PUs). To overcome this problem, existing PAPR reduction techniques for OFDM systems can be applied to NC-OFDM, but they should provide a low PAPR with no side information and relatively low complexity. We consider NC-OFDM with blockwise-subcarrier activation and show that it can intrinsically employ tone reservation (TR) as a PAPR reduction technique. The proposed TR reserves subcarriers within inactive subblocks that are not used by the primary and secondary users. This eliminates data rate loss due to reserved peak reduction tones (PRTs). Further, dynamic PRT allocation in NC-OFDM typically requires side information about the PRT locations to be sent to the receiver. Since we choose PRTs from inactive subblocks, they are simply discarded at the receiver without any side information. The power spectral density (PSD) and bit error rate (BER) are evaluated at the output of the nonlinear PAs to provide a realistic performance comparison.

OFDM has been adopted as a standard for various high data rate wireless communication systems due to several benefits. One of the major drawbacks in OFDM system is its high Peak-to-Average Power Ratio (PAPR) of its transmitted signals thereby making transmitter amplifier to operate beyond its linear range of operation resulting in signal distortion. In this research work a simple method for reducing Peak-to-Average Power Ratio in OFDM is presented. The method is based on Discrete Cosine Transform (DCT) aided successive addition and subtraction (SAS) of data symbols within a single OFDM frame. Performance of the proposed method is evaluated and compared with the existing techniques. Joint reduction in PAPR by combining SAS preprocessed DCT technique and companding is also presented where system utilizes companding technique to further reduce the PAPR of the OFDM signal. Keywords: OFDM; PAPR; DCT; SAS; CompandingOFDM has been adopted as a standard for various high data rate wireless communication systems due to several benefits. One of the major drawbacks in OFDM system is its high Peak-to-Average Power Ratio (PAPR) of its transmitted signals thereby making transmitter amplifier to operate beyond its linear range of operation resulting in signal distortion. In this research work a simple method for reducing Peak-to-Average Power Ratio in OFDM is presented. The method is based on Discrete Cosine Transform (DCT) aided successive addition and subtraction (SAS) of data symbols within a single OFDM frame. Performance of the proposed method is evaluated and compared with the existing techniques. Joint reduction in PAPR by combining SAS preprocessed DCT technique and companding is also presented where system utilizes companding technique to further reduce the PAPR of the OFDM signal. Keywords: OFDM; PAPR; DCT; SAS; Companding

Main disadvantage of a multicarrier communication system is high peak to average power ratio (PAPR) of the transmitted signal. The high PAPR causes the performance degradation due to nonlinear distortion in the high power amplifier (HPA). PAPR value is closely depends on transmitted power and correlation properties of the user’s spreading code. High peak and low average value of the transmitted power increases the PAPR. On the other side high auto correlation function (ACF) value and low cross correlation function (CCF) value of the spreading code also increases the PAPR. But to eliminate the multiple access interference (MAI) in receiver end, ACF should be peak and CCF should be posses zero for all time shifts. So, there is a conflicting nature of PAPR and bit error rate (BER). That’s why an exhaustive effort has been made in this paper for proper distribution of transmitted power within an acceptable range of peak transmitted power and evaluates the new spreading codes using Genetic Algorithms (GA). In general, to obtain optimum PAPR reduction using GA, total searching time to find out the proper amplitude and phase parameters must be accomplished. Simulation results show that PAPR and BER performance using this proposed technique is better than conventional network.

Orthogonal Frequency Division Multiple Access (OFDMA) is a multiple access technique that can accommodate many users with widely varying applications, data rates and Quality of Service requirements, with increased spectral efficiency. Peak to Average Power Ratio (PAPR) reduction for OFDMA is motivated by a desire to increase the mean transmit power and to improve the power amplifier efficiency. This paper presents use of chaotic sequences generated using tent map for multiple data rate spreading and PAPR reduction in OFDMA system. Increase in PAPR due to variable spreading could be reduced by spreading using chaotic sequences. Chaotic sequences gave constant PAPR values for different combinations of data rates. It was also noted that the sequences could be chosen irrespective of the data rates used. Bit error rate was found to be comparable with that for Orthogonal Variable Spreading Factor codes.

In this paper, a Novel Partial Transmit Sequence-based scheme is proposed, namely (N-PTS). The aim is to solve the major hindrance of high Peak to Average Power Ratio (PAPR); as well as to combat the overlapping structure issue affecting Filter Bank Multicarrier system based on the Offset Quadrature Amplitude Modulation (FBMC-OQAM). On that note, computational complexity is also reduced. The proposed scheme uses FBMC-OQAM signal in the frequency domain. To this end, the lowest PAPR value is calculated from data located in a Storage Device (SD). Accordingly, it is properly identified through its location referred to as ’Row’ which consists of the Side Information (SI) to recover the original signal at the receiver. As a result, a substantial reduction in PAPR and computational complexity are achieved. Finally, it is found necessary to mention that SI is claimed not to require extra bits to be transmitted, using phase offset with Minimum Euclidian Distance (MED) criterion, while the Bit Error Rate (BER) performance remains very satisfactory.

Improved PAPR Reduction with Low Complexity in OFDM and Filtered-OFDM (5G) Systems

This paper proposes an enhancement to a previously reported adaptive peak-to-average power ratio (PAPR) reduction method based on clipping and filtering (CF) for eigenmode multiple-input multiple-output (MIMO) - orthogonal frequency division multiplexing (OFDM) signals. We enhance the method to accommodate the case with adaptive modulation and channel coding (AMC). Since the PAPR reduction process degrades the signal-to-interference and noise power ratio (SINR), the AMC should take into account this degradation before PAPR reduction to select accurately the modulation scheme and coding rate (MCS) for each spatial stream. We use a lookup-table-based prediction of SINR after PAPR reduction, in which the interference caused by the PAPR reduction is obtained as a function of the stream index, frequency block index, clipping threshold for PAPR reduction, and input backoff (IBO) of the power amplifier. Simulation results show that the proposed PAPR reduction method increases the average throughput compared to the conventional CF method for a given adjacent channel leakage power ratio (ACLR) even when we assume AMC.

OFDM is an attractive technique for high data rate and reliable communication over fading channels and high peak-to-average power ratio (PAPR) is a notable drawback of orthogonal frequency-division mu ltiplexing (OFDM) systems. The main implementation drawback of this system is the possibility of high Peak to Average Power Ratio (PAPR). The idea in Selective Mapping (SLM) consists of converting the original data lock into several independent signals, and then transmitting the signal that ha s the lowest PAPR. The selected signal index, called side info rmation index, must also be transmitted to allow for the recovery of the data block at the receiver side, which leads to a reduction in data rate. In this paper, we develop a novel SLM PAPR reduction technique. In the novel proposed scheme, the alternative symbol sequences are generated by module 2 additions of data with the rows of cyclic Hadamard matrix with the same size, inserting the selected row’s number to avoi d transmitting any side information and specially using a random-like Irregular Repeat Accumulate (IRA) encoder for both PAPR and Bit Error Rate (BER) better performance. Therefore our proposed scheme in this paper is based on a nove l SLM method combined with a random-like coding of the transmitted data that have no need to use side information for detecting transmitted data in the receiver.